In 2009 the timber industry produced USD $91,898,016,000 in global imports and about USD $89,787,048,000 in exports, indicating it is a sector with high economic impact on the world. In Colombia's case, 2009 saw USD $46 million in wood exports and imports of USD $104.556 million, demonstrating a flaw in timber production to meet domestic demand (TradeMap, 2011).
The main input for wood production are forest species such as oak, pine, eucalyptus, cypress and walnut. The World Bank estimates that some 1.2 billion jobs depend on the forest industry, which is mainly developed in Africa, Latin America and Asia. In Colombia, 70% of the productive forest area consists of introduced species such as araucaria, ash, cypress, various pines, eucalyptus and teak, among others.
Forest plantations of these species are generally located in abandoned and low fertility farmland, which has generated several disadvantages from the initial stages of growth, related to fertilization problems, low percentage of mycorrhization, and a high incidence of disease (Jaramillo & Martinez-Nieto, 2009). All this has led to development and implementation of a variety of products useful in the early growth stages of these species.
In addition, there is currently a high interest for activities involving and use of environmentally sustainable products, such as biofortified substrates and biological inoculants. The latter are understood as products that contain viable beneficial microorganisms used in agriculture for fixing nitrogen, solubilization of nutrient carrier materials, promotion of plant growth, mycorrhizal colonization or transformation of organic matter. These products should not contain microorganisms pathogenic to humans, plants or animals (Pardo, 2002; Soroa et al., 2006; NTC 5842, 2011).
The use of microorganisms in the development of these products is important, as they are the most important soil component and responsible for the dynamics of plant transformation and development. The presence of these microorganisms in soil makes it fertile, that is, increases the concentration of nutrients available to the plant or microbial populations that release nutrients and allow good plant development.
Among the microorganisms, bacteria and arbuscular mycorrhizal fungi have been recognized by the Food and Agriculture Organization-FAO as an important tool to increase agricultural production and provide benefits to plants in protection and obtaining of nutrients (Ocampo et al., 2001). Some characteristics of these microorganisms are that they do not require internal colonization of plant tissues to act; having the ability to increase their population density in the rhizosphere in a short time after inoculation; and effectively colonizing the root surface (Jimenez et al., 2001).
In the specific case of fungi, the most important advantages are evident in the increased capacity to obtain phosphorus and in improvement of water relations and adaptation to soil by plants produced in the nursery (Ocampo et al., 2001). The bacteria in turn promote interaction between plant roots and fungi, bioprotective action, and plant development, and are involved in the production of plant growth regulators such as 3-indole acetic acid (IAA); they also facilitate the assimilation of nitrogen and inorganic salts. Other advantages are associated with increased vigor, emergence and seedling weight and further development in root systems, and an increase of up to 30% in production (Jimenez et al., 2001; Bertolini et al., 2007).
Regarding the species Pseudomonas sp. and Enterobacter sp., they have been used as bio-fertilizers or growth promoters in Lactuca sativa (Kohler, 2009), tomato (Gamalero, 2002, Pivato et al., 2009), in Medicago truncatula, in tobacco (Ramamoorthy et al., 2001) and in rice (Nandakumar, 2001), among others.
Regarding Enterobacter sp., it was revealed that has been used in promoting growth in canola (Saleh, 2001; Mayak, 2001; Nie et al., 2002), tomato (Holguin, 2003), carnation (Li et al., 2005) and sugar cane (Mirza et al., 2001), among others.
The passage of nutrients, oxygen transfer and adhesion of a microbial population to plants is favored by using microbial media. Using media is important because, when introducing microorganisms to different environments without a support, they can have low survival rates for the first ones and a low efficiency due to the low number of colony forming units per gram of soil. Use of supports allows greater survival in inoculation processes and yet does not cause pollution in the environment in which they are applied. Such microbial supports are also known as microbial carriers.
However, some limitations arise when using certain media. For example, when peat is used as a support, in addition to its high cost and low availability in our tropical countries, we note the low purity in the support, since after 90 days of cold storage inoculants begin to show contamination with various microorganisms other than those immobilized (Stephens & Rask, 2000), such as Gram-positive bacilli. With bamboo sawdust, cell viability is not maintained, and in the case of a sodium alginate support, although the purity, viability and biological activity are maintained, the costs of obtaining the inoculant are high.
Within the supports used for this purpose, the prior art discloses different types, according to the compounds of porous materials such as polyurethane, cellulose, polypropylene and ceramics. These supports are characterized because they allow immobilizing cells of animals, plants, microorganisms and protozoa. Cellulose supports are susceptible to erosion, therefore their duration is shorter, and ceramic supports have several limitations due to their high specific gravity which prevents them from being fluid in water.
Another type of supports is composed of gels, including compounds for polyacrylamide, polyethylene glycol and alginic acid. The gel supports may contain large quantities of water, so they have greater biocompatibility with microorganism, human and plant cells.
For promotion of plant growth and the agriculture industry, the most commonly used supports are clay, vermiculite, perlite, sepiolite, kaolin, diatomaceous earth, and natural zeolite, among others, as shown in patent application WO2009/027544A1.
Other inventions relating to the use of supports, where sawdust is used, have been identified in the prior art, such as Patent Document JP2000016889 that relates to a process for the production of manure as a fermentation fertilizer using photosynthetic bacteria of the genera Rhodopseudomonas, Rhodospirillum and Ectothiorhodospira, and the families Ectothiorhodospiraceae and Chloroflexaceae, with acetic acid or a material containing it, and in which the mixture on a porous material (30% w/w or less) is used as adsorbent produced by carbonization of wood, sawdust, coconut shells, bagasse, wheat hulls, cottonseed hulls, coffee grounds or the like, a zeolite, etc.
Importantly, this document merely discloses the requirement of a 30% (w/w) or less microbial culture with respect to the porous material. Also, this formulation includes a requirement of acetic acid or a source thereof in a ratio of up to eight times the volume of the culture. However, it does not establish a level of particular microorganisms per gram, thus preventing precision dosing of the product's components.
Patent KR960002627 reveals a composting promoter obtained by mixing a uniform part of bacteria with sawdust, rice husks and limestone in proportions (w/w) 4:5:1.
Patent KR920003238 discloses an agent for soil improvement obtained by mixing 94-97% (w/w) of organic waste matter, 2-5% (w/w) of sawdust, 0.2-0.5% of whitewash and 0.2-0.5% ash wood and adjusting the pH to a value between 6.5 and 7.5.
Patent JP11029384 reports an organic fertilizer that promotes plant growth, effectively improves soil quality and allows the reuse of industrial waste. This fertilizer is obtained by mixing rice bran, sawdust from a foliage tree or wood, liquid soy sediments, cut rice plant straw, waste garbage or granular charcoal, with a material comprising a bacterial debris from mushroom cultivation (e.g. Shiitake, Maitake and Shimeji) and fermenting the resulting material.
Patent JP4122788 refers to a soil activator and plant growth promoter obtained by aerobic fermentation of a vegetable source rich in fibers mixed with bran cereal, shellfish fossils, among others, and an enzyme complex, which is mixed with sawdust or enzymatically treated wood chips.
Patents KR960002627 and JP11029384 report separate stages, as in the case of preparing the support (heating and carbonization) and stages of inoculation and incubation, respectively.
According to the above information, there clearly still remains a need for biological inoculants for nursery substrates in order to promote plant growth without affecting the environment and allowing plants to achieve best features of vigor and health in less time, through a process that includes stages of preparing the support, inoculation and incubation, and allowing reduced use of chemical fertilizers.